The present invention relates to a color conversion filter manufacturing method. In particular, it relates to a method for manufacturing a color conversion filter including a color conversion layer having a high-resolution pattern.
One way of achieving multicolor emission with an organic electroluminescent element is by a color conversion system. In a color conversion system, multiple colors are achieved by providing, on the front surface of an organic electroluminescent element, a color conversion layer that absorbs the light emitted by the organic electroluminescent element, converts the wavelength distribution and radiates light having a different wavelength distribution. Color conversion systems are easy to manufacture because the organic electroluminescent element is of one kind (single color), and applications to large-scale displays are being intensively investigated. Another advantage of color conversion systems is that good color reproducibility can be obtained by further combining color filter layers that transmit light in specific wavelength bands.
As such a color conversion layer, Japanese Patent Application Laid-open No. H8-286033 (Patent Document 1) discloses a configuration including a fluorescent dye dispersed in a polymer resin. In order to obtain sufficient efficiency with the proposed resin dispersion-type color conversion layer, however, the color conversion layer must be about 10 μm thick. In addition, forming the organic electroluminescent element on the upper surface of the color conversion layer requires special technology, including a technique for flattening out the irregularities on the upper surface of the color conversion layer and a technique for blocking moisture produced from the color conversion layer. All of these increase costs.
To resolve the problems of resin dispersion-type color conversion layers, Japanese Patent Application Laid-open Nos. 2002-75643 and 2003-217859 (Patent Documents 2 and 3) disclose methods for forming color conversion layers that do not contain resin by vapor deposition, sputtering and other dry processes. The problem with these methods is that although they can form color conversion layers with thicknesses of 2 μm or less, high-definition patterning (150 ppi or more for example is difficult.
Japanese Patent Application Laid-open Nos. 2004-253179, 2006-73450, 2006-32010, 2003-229261 (Patent Documents 4 to 7) and the like propose the inkjet method as a method for forming a color conversion layer with a small film thickness and a high-definition pattern. The advantage of forming a color conversion layer by the inkjet method is that the costs of forming the color conversion layer can be controlled because the ink utilization efficiency is extremely high.
Forming a high-definition pattern by the inkjet method requires precise discharge of tiny droplets, and this in turn requires low-viscosity ink. Consequently, the solids content cannot be too high since this is a cause of increased viscosity, and the volume of ink droplets needs to be large in order to obtain the necessary film thickness. As a solution for increasing the volume of ink droplets, Japanese Patent Application Laid-open No. 2000-353594 (Patent Document 8) proposes a method for forming a bank on a substrate. According to Patent Document 8, both the shape of the bank and the wetting properties of the bank surface need to be controlled in order to form a high-definition pattern. Specifically, the bank surface must be liquid-repellent with respect to the ink, while the underlying surface (that is, the ink receiving surface) must be lyophilic with respect to the ink. Patent Document 8 also describes a method that includes (a) a step of forming a bank using two materials having different wetting properties, and (b) a step of plasma processing (fluorine plasma/oxygen plasma) in which multiple gasses are used and the mixing ratios of these gasses are controlled in order to control the wettability of the bank surface and form a high-definition pattern.
Alternatively, Japanese Patent Application Laid-open No. 2007-102030 (Patent Document 9) proposes a method for improving the lyophilicity of the substrate surface for the ink by subjecting a substrate with a black matrix formed thereon to atmospheric pressure plasma treatment in a mixed gas atmosphere of carbon dioxide and a noble gas when forming a color filter layer by the inkjet method using a black matrix as a separation wall (Patent Document 9). This method requires complex control of the gas mixing ratio and the like during atmospheric pressure plasma treatment.
Japanese Patent Application Laid-open No. 2003-229261 (Patent Document 7) proposes a method using a wetting property changing layer. This method includes a step of forming a wetting property changing layer so as to cover a substrate and a separation wall formed on the substrate, and a step of exposing only the part of the wetting property changing layer in contact with the substrate through a second substrate containing a photocatalyst-containing layer to thereby improve the lyophilicity of the wetting property changing layer of the exposed region for the ink. Because only the part of the wetting property changing layer that contacts the substrate is exposed in this method, it requires a mask aligned with the separation wall in the exposure step. This makes processing complex.
Japanese Patent Application Laid-open No. 2005-156739 (Patent Document 10) proposes a method for preparing a pattern formed body including a liquid-repellent part and a lyophilic part by patterned exposure of a layer containing a photocatalyst and an organic polysiloxane as a liquid repellency imparting agent. According to Patent Document 10, it is possible to prepare the pattern formed body with a color filter, metal wiring, organic electroluminescent layer, biochip or the like on the pattern formed body.    Patent Document 1: Japanese Patent Application Laid-open No. H8-286033    Patent Document 2: Japanese Patent Application Laid-open No. 2002-75643    Patent Document 3: Japanese Patent Application Laid-open No. 2003-217859    Patent Document 4: Japanese Patent Application Laid-open No. 2004-253179    Patent Document 5: Japanese Patent Application Laid-open No. 2006-73450    Patent Document 6: Japanese Patent Application Laid-open No. 2006-32010    Patent Document 7: Japanese Patent Application Laid-open No. 2003-229261    Patent Document 8: Japanese Patent Application Laid-open No. 2000-353594    Patent Document 9: Japanese Patent Application Laid-open No. 2007-102030    Patent Document 10: Japanese Patent Application Laid-open No. 2005-156739